How Body Age Works
Body Age is a wellness estimate based on recent sleep, activity, and fitness signals. It is designed to make longer-term patterns easier to understand. It is not a diagnosis and does not judge your health from a single day.
Seven Metrics, Three Dimensions
| Dimension | Metrics |
|---|---|
| Sleep | Sleep duration and sleep regularity |
| Activity | Aerobic duration, high-intensity duration, and daily steps |
| Fitness | VO2 max and resting heart rate |
Each available metric is scored using its current in-app rule. The metrics are combined within their dimension, converted to an age adjustment, and then combined with actual age. Missing metrics are excluded instead of being replaced with guessed values.
How to Read Aging Rate
Aging rate normalizes the difference between Body Age and actual age. A value near 1x means the two are close, below 1x means the current baseline is younger, and above 1x means it is older. The displayed range is 0–3x.
This is not a week-over-week change rate. Use the trend interpretation below the gauge to understand whether the recent Body Age difference is improving, stable, or needs attention.
Data Windows and Availability
- Sleep uses up to seven valid nights from the past 14 days and needs at least three valid nights.
- Activity covers the most recent seven-day window.
- VO2 max uses a representative recent value from a 30-day window.
- Resting heart rate uses the last seven completed calendar days.
- At least two of the three dimensions must be available before Body Age is shown.
Apple Health permissions, Apple Watch wear time, source priority, battery, and recent sample availability can affect which metrics are included.
Missing Data
A missing metric does not receive a zero and is not estimated. Yuelu recalculates the available weights so incomplete data does not unfairly dominate the result. If too few dimensions are available, the page reports insufficient data instead of producing a Body Age.
Health Notice
Body Age and aging rate are for wellness education and product explanation only. They are not medical diagnoses or treatment advice. Consult a qualified clinician for persistent symptoms or health concerns.